This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application MASK FOR COLOR PICTURE TUBE filed with the Korean Industrial Property Office on Jul. 12, 2000 and there duly assigned Ser. No. 39984/2000.
1. Technical Field
The present invention relates to a color picture tube, and more particularly, to a mask which is installed close to a fluorescent film at the inner side of a panel and performs a color selection function.
2. Related Art
In a color picture tube adopted in computer monitors or televisions, three electron beams are emitted from an electron gun and pass through electron beam passing holes of a mask having a color selection function. Then, the electron beams land on red, green and blue fluorescent substances on a fluorescent film formed on a screen surface of a panel to excite the fluorescent substance so that an image is formed.
In the above color picture tube for forming an image, the mask having a color selection function is divided into a dot mask used for computer monitors and a slot mask (or a slit mask) used for televisions. Since the screen surfaces are formed to have predetermined curvatures considering landing of deflected electron beams, the dot mask and slot mask are designed to have curvatures corresponding to those of the screen surfaces.
The above masks are formed of a thin plate having a thickness of 0.1 through 0.25 millimeters (mm) and a plurality of electron beam passing holes are formed therein by etching the thin plate. Then, the thin plate is formed to have a predetermined curvature. When the mask does not have a predetermined curvature or more, mechanical intensity of the mask deteriorates so a permanent plastic deformation can be generated to the mask due to impacts occurring during production of picture tubes or transfer thereof. As a result, the color selection function which is an intrinsic function of the mask may not be properly performed. Also, the mask formed to have a predetermined curvature is supported by a frame installed on an inner surface of the panel. The mask is easily heated by thermions emitted by the electron gun and thermally expands. Accordingly, a doming phenomenon occurs so that the color selection function with respect to the three electron beams cannot be performed.
As the size of a color picture tube recently increases, an image is distorted due to the curvature of a screen surface and a natural image does not get smoothly represented, so that a flat screen surface is required.
Slot type masks for preventing the doming phenomenon and enabling a flat screen surface are disclosed in U.S. Pat. No. 3,638,063 to Tachikawa et al., entitled GRID STRUCTURE FOR COLOR PICTURE TUBES, issued on Jan. 25, 1972, U.S. Pat. No. 4,942,332 to Adler et al., entitled TIED SLIT MASK FOR COLOR CATHODE RAY TUBES, issued on Jul. 17, 1990, U.S. Pat. No. 4,926,089 to Moore, entitled TIED SLIT FOIL SHADOW MASK WITH FALSE TIES, issued on May 15, 1990, and U.S. Pat. No. 4,973,283 to Adler et al., entitled METHOD OF MANUFACTURING A TIED SLIT MASK CRT, issued on Nov. 27, 1990. Of the disclosed masks, an aperture grille type mask is shown in FIG. 1.
Referring to FIG. 1, the aperture grille type mask 10 includes strips 11 which are separated a predetermined distance from one another and parallel to each other and form slots. In the mask 10, both end portions of each of the strips 11 are supported at a frame 12 to have tension. Each of strips 11 contacts damper wires 13 to prevent independent vibration of each strip. However, such a mask is difficult to handle during a manufacturing process since it has a structure in which the strips 11 are parallel to each other and only both end portions of the strips 11 are fixed.
To solve the above problem, as shown in FIG. 2, an example of a slot type mask has been suggested in U.S. Pat. No. 4,942,332. As shown in the drawing, in the slot type mask, a plurality of strips 22 and 22xe2x80x2 forming a slit 21 are formed on a thin plate by being separated a predetermined distance and the strips 22 and 22xe2x80x2 are connected by tie bars 23. Thus, since the strips 22 and 22xe2x80x2 are connected by the tie bars 23, howling generated by vibrations due to impacts and sonic waves applied from the outside can be slightly reduced. Nevertheless, the howling reducing effect cannot be expected much since the vibrations of the tie bars 23 are transferred by the tie bars 23 through the neighboring strips.
FIG. 3 shows a mask having false ties disclosed in U.S. Pat. No. 4,926,089. As shown in the drawing, in a mask 30, strips 31 and 31xe2x80x2 installed parallel to each other is connected by a tie bar 32 for forming a slot 33. A plurality of false ties 34 extending from the strips 31 and 31xe2x80x2 and not contacting the adjacent strops 31 and 31xe2x80x2 are positioned in the slot 33 between the tie bars 32.
In the above mask 30, visibility of an image is improved by disposing the false ties 34 between the tie bars 32. However, since the strips 31 and 31xe2x80x2 are connected by the tie bars 32, a problem that vibrations generated by an impact applied to a portion are transferred to a neighboring strip cannot be solved.
In particular, in the above mask type, a moire phenomenon occurs because scanned electron beams and the holes of the mask are interfered with each other. The moire phenomenon becomes serious at the peripheral portion of a screen because the shape of a spot of an electron beam landing on a fluorescent film is deformed to be horizontally elongated due to a strong pincushion magnet field by a deflection yoke as a deflection angle of an electron beam increases. Accordingly, methods of selecting a mask pitch at which the moire phenomenon is minimized or reducing a vertical pitch to reduce is used to reduce the depth of modulation, are used. However, the above methods are not recommended because transmissivity at the periphery portion of the mask is lowered and the brightness of a screen is not uniform.
Also, in the mask method, a mask doming phenomenon becomes serious as the mask is heated by the electron beams. Furthermore, the doming phenomenon easily occurs at the peripheral portion of a mask. In the case of a tension mask, when a steel frame which is cheap is used, the mask including a mask bridge portion extends in a horizontal direction so that color escape in a wrinkle shape is generated on a screen.
To solve the above problems, it is an object of the present invention to provide a tension mask for a color picture tube which can improve a vibration reduction effect by reducing transfer of vibrations between electron beam strips.
It is a further object of the present invention to provide a tension mask which can reduce a moire phenomenon due to interference between the scanned electron beam and holes of a mask and reduce a doming phenomenon of the mask, and improve brightness of an image.
Accordingly, to achieve the above objects and others, there is provided a tension mask for a color picture tube comprising a plurality of strips separated a predetermined distance from each other and parallel to each other, and a plurality of real bridges for connecting the neighboring strips and forming slots through which electron beams pass, the number of the real bridges gradually decreasing from the central portion of the tension mask to the peripheral portion thereof. The electron beams pass through the slots or penetrate the slots.
It is preferred in the present invention that the real bridge is not formed between an end strip located at the outermost portion of the tension mask in a horizontal direction and a strip adjacent thereto.
Also, it is preferred in the present invention that a plurality of dummy bridges extending from the strips in the opposite directions to face each other but not physically contacting each other, are disposed between the real bridges connecting the strips.
Also, to achieve the above objects and others, there is provided a tension mask for a color picture tube comprising a real ridge area located at the central portion of the tension mask, in which a plurality of strips separated a predetermined distance from each other and parallel to each other and a plurality of real bridges for connecting the neighboring strips and forming slots through which electron beams pass, the number of the real bridges gradually decreasing from the central portion of the tension mask to the peripheral portion thereof, are formed, and a dummy bridge area located at the peripheral portion of the tension mask, in which a plurality of dummy bridges extending from at least one side of each of the strips but not physically contacting the opposite strip, are formed, wherein the tension mask is a hybrid type. When the term xe2x80x9chybrid typexe2x80x9d is used to describe the tension mask, that tension mask is a combination of a real bridge area, a dummy bridge area, and an aperture grill area.
It is preferred in the present invention that the dummy bridge area further includes real bridges for connecting the neighboring strips, the number of the real bridges gradually decreasing from the central portion of the tension mask to the peripheral portion thereof.
Alternatively, to achieve the above objects and others, there is provided a tension mask for a color picture tube comprising a real bridge area located at the central portion of the tension mask, in which a plurality of strips separated a predetermined distance from each other and parallel to each other and a plurality of real bridges for connecting the neighboring strips and forming slots through which electron beams pass, the number of the real bridges gradually decreasing from the central portion of the tension mask to the peripheral portion thereof, are formed, and a dummy bridge area located at the peripheral portion of the tension mask, in which a plurality of dummy bridges extending from at least one side of each of the strips but not physically contacting the opposite strip, are formed, and an aperture grille area located around the dummy bridge area and having a single slot formed by the strips, wherein the tension mask is a hybrid type.
To achieve these and other objects in accordance with the principles of the present invention, as embodied and broadly described, the present invention provides a tension mask apparatus for a color picture tube, the apparatus comprising: a plurality of strips being separated a predetermined distance from each other and being substantially parallel to each other; and a plurality of real bridges connecting adjacent ones of said strips and forming slots through which electron beams pass, a quantity of said real bridges gradually decreasing from a central portion of said tension mask to a peripheral portion of a tension mask.
To achieve these and other objects in accordance with the principles of the present invention, as embodied and broadly described, the present invention provides a tension mask apparatus for a color picture tube, the apparatus comprising: a first plurality of strips being separated a predetermined distance from each other and being parallel to each other, said first plurality of strips being located in a real bridge area, said real bridge area being located at a central portion of a tension mask; a plurality of real bridges connecting adjacent ones of said first plurality of strips and forming first slots separating said first plurality of strips, a number of said real bridges gradually decreasing in a first direction from said central portion of said tension mask toward a peripheral portion of said tension mask, said plurality of real bridges being located in said real bridge area; a second plurality of strips being separated a predetermined distance from each other and being parallel to each other, said dummy bridge area forming second slots separating said second plurality of strips, said second plurality of strips being located in a dummy bridge area, said dummy bridge area being located at said peripheral portion of said tension mask; and a plurality of dummy bridges, each of said dummy bridges extending in opposite directions into said second slots from adjacent ones of said second plurality of strips, said plurality of dummy bridges being located in said dummy bridge area, said tension mask being a hybrid type tension mask.
To achieve these and other objects in accordance with the principles of the present invention, as embodied and broadly described, the present invention provides a tension mask apparatus for a color picture tube, comprising: a plurality of strips being separated a predetermined distance from each other and being parallel to each other; a real bridge area being located at a central portion of a tension mask, said real bridge area comprising a plurality of real bridges connecting neighboring ones of said strips in said real bridge area and forming slots through which electron beams pass, said real bridges being formed to gradually decrease in number in a direction from said central portion of said tension mask to a peripheral portion of said tension mask; a dummy bridge area being located at said peripheral portion of said tension mask, said dummy bridge area comprising a plurality of dummy bridges extending from at least one side of each of said strips in said dummy bridge area and not physically contacting the opposite strip; and an aperture grille area being located near said dummy bridge area and having at least one slot formed by said strips, said tension mask being a hybrid type.
The present invention is more specifically described in the following paragraphs by reference to the drawings attached only by way of example. Other advantages and features will become apparent from the following description and from the claims.